//阻塞队列
public class BlockingQueue {
    private int[] items = new int[1000];
    private volatile int size = 0;
    private volatile int head = 0;
    private volatile int tail = 0;

    public void put(int value) throws InterruptedException {
        synchronized (this) {
            // 此处最好使⽤ while.
            // 否则 notifyAll 的时候, 该线程从 wait 中被唤醒,
            // 但是紧接着并未抢占到锁. 当锁被抢占的时候, 可能⼜已经队列满了
            // 就只能继续等待
            while (size == items.length) {
                wait();
            }
            items[tail] = value;
            tail = (tail + 1) % items.length;
            size++;
            notifyAll();
        }
    }

    public int take() throws InterruptedException {
        int ret = 0;
        synchronized (this) {
            while (size == 0) {
                wait();
            }
            ret = items[head];
            head = (head + 1) % items.length;
            size--;
            notifyAll();
        }
        return ret;
    }

    public synchronized int size() {
        return size;
    }

    // 测试代码
    public static void main(String[] args) throws InterruptedException {
        BlockingQueue blockingQueue = new BlockingQueue();
        Thread customer = new Thread(() -> {
            while (true) {
                try {
                    int value = blockingQueue.take();
                    System.out.println(value);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "消费者");
        customer.start();
        Thread producer = new Thread(() -> {
            Random random = new Random();
            while (true) {
                try {
                    blockingQueue.put(random.nextInt(10000));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
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        }, "⽣产者");
        producer.start();
        customer.join();
        producer.join();
    }
}
